Contact lenses are disposed in direct contact with and over the cornea of an eye to correct a patient's vision. In many cases, the patient wears the contact lens for several hours or days and then removes the lens for cleaning, storage, and reuse. The lens is placed into a well formed in a lens case, and the well is filled with a multipurpose solution formulated to include various additives, such as an antimicrobial, disinfectant, and/or preservative for reducing the microbial load that has built up on the lens. After cleaning, the lens is removed from the well and directly inserted into the eye.
As is typically the case, many different types of microorganisms can be found on a contact lens and/or in a contact lens case after use. One of the most disinfectant-resistant microorganisms, Candida albicans (“C. albicans”), is a diploid fungus that serves as a pathogen producing colonies of yeast on a surface. The colonies form a biofilm on the contact lens which without cleansing and disinfecting may lead to infection or diseased conditions of the eye. Other microorganisms, such as gram negative bacteria, may be present after wear and may increase the incidence of inflammatory cells or infiltrates invading the cornea. Infiltrates can result in discomfort and intolerance to contact lens wear.
To reduce and/or prevent the likelihood of infection, the multipurpose solution is formulated to be sufficiently strong to be capable of killing unwanted microorganisms, including C. albicans. Additionally, various other factors are considered during formulation of the multipurpose solution. For example, an ideal solution preferably also is compatible with a variety of different contact lens materials, such as silicone hydrogel and the like. Contact lens compatibility can be measured by contact lens discoloration, physical parameter change, fragility, and uptake/release of solution components, such as antimicrobial components. Moreover, the lens solution is preferably further formulated such that ocular surface cell changes, irritation or user discomfort is minimized during use.
Balancing the aforementioned factors continues to be a challenge when formulating the multipurpose solution. In particular, the addition of more disinfecting agents increases a solution's efficacy, but too large an increase in disinfecting agent concentration usually reduces contact lens material compatibility and/or ocular comfort or produces adverse changes in corneal epithelial ocular surface cells, such as cell death commonly known as corneal epithelial punctate fluorescein staining Formulating a solution with less disinfecting agent in turn results in a solution with lower antimicrobial efficacy. Furthermore, disinfecting agents are known to be absorbed into contact lenses themselves, further decreasing a solution's efficacy. Although increasing the concentration of disinfecting agent alleviates the absorption issue, too much disinfecting agent can cause eye irritation, increased corneal epithelial staining and/or presence of infiltrates.
Accordingly, there is a need for a contact lens multipurpose solution that not only provides a desired amount of biocidal efficacy against resistant microorganisms, such as C. albicans and other endotoxic bacteria, but does so with minimized ocular discomfort to the patient. Additionally, there is a need for a multipurpose solution that maintains a sufficiently high disinfectant potential while reducing an incidence of infiltrates and/or corneal staining.